Summary:
This commit completely refactors `DeltaStreamingConnection`, notably
introducing the following changes:
- Right now, `AccountDeltaConnection` establishes both delta connections to the cloud api and to the `client-sync` database (K2). This class is meant to disapper in favor of splitting into two different classes meant for syncing with the n1Cloud api and the local database. Specifically, `DeltaStreamingConnection`'s only responsibility is now to connect to the n1Cloud API and establish an http streaming connection for metadata deltas, etc. This class no longer unecessarily inherits from `NylasLongConnection`, which removes a lot of unecessary callback indirection.
- The statuses of the n1Cloud delta streaming connections are now stored in as JSONBlobs in edgehill.db under new keys. This commit ensures that the data is correctly migrated from the old key (`NylasSyncWorker:<account_id>`).
- The `DeltaStreamingConnection` now correctly retries when closed or errors. This logic previously existed, but was removed during the K2 transition: https://github.com/nylas/nylas-mail/blob/n1-pro/internal_packages/worker-sync/lib/nylas-sync-worker.coffee#L67
- Delta connection retries now backoff using the `ExponentialBackoffScheduler`
- Attempt to restore the delta connection whenever the app comes back online
Depends on D4119
Test Plan: manual + planned unit tests in upcoming diff
Reviewers: halla, mark, evan, spang
Reviewed By: evan
Differential Revision: https://phab.nylas.com/D4120
